1. Field of the Invention
The present invention generally relates to the marking of a decoration on an object, such as, by way of a non-limiting example, a gambling chip having the shape of a disk or a plate. A gambling chip, also referred to as a casino chip, should be understood as any element that can be used in a gambling hall, and represents a nominal value which may or may not be predetermined. Generally speaking, these chips are made of a rigid and scratch-resistant plastic.
2. Discussion of Background Information
Gambling chips are, almost systematically, given a decoration by marking on their faces and/or sides, and this decoration, depending on the end uses of the chips, possibly ranging from the simplest to the most complex. In the following disclosure, the term “decoration” should be understood in its broadest sense and includes any design, symbol, mark and characters (for example, letters, numerals, bar codes or various codings) capable of graphical representation and/or visual or optical effect (for example, by the use of UV-sensitive ink). More specifically, the decoration of chips is capable of fulfilling at least one of the many functions presented briefly below:    i) identifying the chip and/or chip value and/or casino and/or gambling table and/or player;    ii) providing decoration having an aesthetic character and/or acting as an advertising medium; and    iii) authenticating the chip and providing security against the risks associated with falsification and/or fraudulent reproduction.
With respect to the marking itself, it is possible to distinguish thickness or volume marking in the body of the chip (for example, marking within the bulk with or without insert, etching, multi-shot injection molding of the chip body made of plastic, etc.), from the marking of a surface (for example, printing using monochrome or polychrome screen printing). The invention relates more particularly to surface marking.
Among surface marking techniques for gambling chips, a so-called “sublimation” technique is known. According to this technique, which is illustrated in FIG. 3, a tracing paper, paper foil, screen or transfer (for example, made of paper or fabric) on which the pigmented layer or decoration (which may be multicolor) has been printed, generally by screen printing, is placed on one face of the chip or plastic body (step 1). The chip and tracing paper or transfer are then arranged in a hot press (step 2), the printed side of the transfer being pressed on the face of the chip. Through the application of heat, the ink of the transfer is sublimed so as to be deposited on the outer surface of the chip and to migrate into the plastic material of the chip to a depth of several tens of microns, the transfer paper acting as a retaining screen for the pigment vapors. Generally, the sublimation temperature of the colored pigments is between 140° C. and 180° C., depending on the colors and inks. The paper foil is then removed (step 3). This technique, which yields good results with respect to the adherence of the decoration, is not very accurate due to the passage by transfer, and is quite difficult to implement due, in particular, to the risks of deformation of the transfer paper during passage in the hot press. Furthermore, it requires subliming each face of the chip and the side separately (the sublimation of the side being achieved, for example, by heating the chips stacked in a supporting tube which is internally fitted with the transfer paper). Finally, it must be noted that the marking technique by sublimation is limited neither to gambling chips in general, nor to the marking support-objects having a body made of plastic (in this latter case, the body, for example, made of metal, is covered with a surface coating made of plastic, for example, a plastic varnish, prior to the sublimation).
The commonly owned published International Application WO-A-96/25066 and U.S. Pat. No. 5,794,532, the disclosure of which is hereby expressly incorporated by reference in its entirety, describes the use of pad-printing for the surface marking of the faces and/or the side of chips. More particularly, this document describes the marking of each face of the chip by pad-printing using an inked pad which is displaced coaxially with the chip with marking of the side with a inking pad-drum or, for chips having a soft-profiled side, a marking of a portion of the side corresponding to the chamfered or rounded edge of the face of the chip. This technique is very satisfactory with respect to the quality and accuracy of the decoration (pad-printing allowing half-tones or screen rulings of 175 against 100–120 by screen printing), but the decoration applied to the surface sometimes requires a protective varnish at the end of the chip manufacture.